Data Communications
     The term telecommunication means 
           term telecommunication means 
      communication at a distance. The word data 
      communication at a distance. The word data 
      refers to information presented in whatever 
      refers to information presented in whatever 
      form is agreed upon by the parties creating 
      form is agreed upon by the parties creating 
      and using the data. Data communications are 
      and using the data. Data communications are 
      the exchange of data between two devices 
      the exchange of data between two devices 
      via some form of transmission medium such 
      via some form of transmission medium such 
      as a wire cable. 
      as a wire cable. 
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     Fundamental Characteristics
      The effectiveness of a data communication 
       system depend on four fundamental 
       characteristics:
        Delivery
        Accuracy
        Timelines
        Jitter
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     Five Components of Data 
     Communication
                                 1.  Message
                                 2.  Sender
                                 3.  Receiver
                                 4.  Medium
                                 5.  Protocol
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     Direction of data flow
                                                Simplex
                                                Half Duplex
                                                 Full Duplex
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     Networks: key issues
      Network criteria
         Performance
           Throughput
           Delay
         Reliability
           Data transmitted are identical to data received.
           Measured by the frequency of failure
           The time it takes a link to recover from a failure  
         Security
           Protecting data from unauthorized access
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